This invention relates to a method of operating a switching arrangement for initiating a transfer of data into a data input device seized over an interoffice trunk in a distant exchange during a telephone connection established over an interoffice trunk between two central offices. The invention has particular application to a telephone connection established over an exchange line between a subscriber of a private branch exchange and a subscriber of a telephone system. In the latter an identification in the repeater allocated to the interoffice trunk, emitted more particularly to the private branch office during the call in progress from a telephone set, brings about a condition initiating a new call and the connection of a central control unit to the repeater. The input equipment for accepting the data selected by an extension user is connected as a result of a loop interruption of specified duration of the speech path.
There is disclosed in U.S. Pat. No. 3,427,404 a switching arrangement wherein upon dialing each digit a selection preparation signal is transmitted which normally initiates in the repeater during the cell setup the connection of a central pulse receiver and which, after the call has been established, initiates in dependence on the existing switching condition a connection changeover during the call in progress. This means that during the call in progress one can initiate with the selection preparation signal a call-back interruption in dependence on the call condition in the repeater. Hence, during the call in progress one can with the aid of the known switching arrangement being about from a telephone set a call transfer, depending on the circuit condition in the repeater. However, with this switching arrangement no selective transfer of another signal over the interoffice trunk is possible.
It is an object of this invention to provide a method for enabling with minimum additional expense in a repeater allocated to an interoffice trunk the connection of a data input device seized in a distant exchange over an interoffice trunk for data transferred from a telephone set.